I saw a question about photos repeating when randomised.
The answer seemed to relate to the pro edition.

I'm using the free edition in a similar way with several thousand photos, and I also notice that
photos seem to repeat. I have got the "At the end of the show rebuild the file list" option ticked, so that's not the issue.

I have used several random photo show screen savers and they all seem to do the repeat thing so I suspect that it's
an issue with the randomising algoritim.

I've tried to do the file list thing as per FAQ25 but my version doesn't have an option to include shortcut to file list (*.glst) option.
The only option only offers shortcut folders (*.ink), which I have got ticked.
I have my *.glst file in a folder which is the only one in the folder list, but I get an error message "can't find any file to show in the configured folder list"

There is no way to prevent photos from repeating when using gPhotoShow Free Edition and random display mode. The Free edition uses a simple randomization algorithm and repetitions are always possible regardless of the algorithm used. The Pro edition keeps a list of photos to display and removes photos from this list once they have been shown. In this way photos never repeat.
Image lists (.glst files) are supported only by the Pro version only.

So, if I upgrade to the pro version I won't get repeats because
1) the algorithm is different and it saves a file list to work from, and
2) the *.glst feature will work. (although I shouldn't need to use it)

The answer is yes to both question. In addition you can try gPhotoShow Pro freely for 30 days before you purchase a license, then if you don't like it you can go back to the free version. In any case feel free to write again or if you have any issue with the Pro version.

Just a helpful addition to the thread.
I bought the pro version and got it running.
The difference was almost immediate!
Within the first couple of hours I saw photos in my collection that I haven't seen for months
using any other random photo free screen saver, including this one, or noticed any repeats.
So, if you want a true random photo display without those annoying "favourite photo repeats"
then pay up and buy the pro version!